1. Field of the Invention
This invention relates to medical devices and more particularly relates to the working end of an electrosurgical instrument that is adapted for sealing or welding tissue that is engaged between paired jaw members. More specifically, the elongate jaw members carry electrodes with engagement surfaces that provide a resistive gradient for causing controlled heating of engaged tissue.
2. Description of the Related Art
In various open and laparoscopic surgeries, it is necessary to weld or seal the margins of transected tissue volumes, for example, in a lung resection. In some procedures, stapling instruments are used to apply a series of mechanically deformable staples to seal the transected edge a tissue volume. Such mechanical devices may create a seal that leaks which can result in later complications.
Various radiofrequency (Rf) surgical instruments have been developed for sealing the edges of transected tissues. For example, FIG. 1A shows a sectional view of paired electrode-jaws 2a and 2b of a typical prior art bi-polar Rf grasper grasping two tissue layers. In a typical bi-polar jaw arrangement, each jaw face comprises an electrode and Rf current flows across the tissue between the first and second polarities in the opposing jaws that engage opposing exterior surfaces of the tissue. FIG. 1A shows typical lines of bi-polar current flow between the jaws. Each jaw in FIG. 1A has a central slot adapted to receive a reciprocating blade member as is known in the art for transecting the captured vessel after it is sealed.
While bi-polar graspers as in FIG. 1A can adequately seal or weld tissue volumes that have a small cross-section, such bi-polar instruments are often ineffective in sealing or welding many types of anatomic structures, e.g., (i) anatomic structures having walls with irregular or thick fibrous content, such as lung tissue; (ii) bundles of disparate anatomic structures, (iii) substantially thick anatomic and structures, and (iv) large diameter blood vessels having walls with thick fascia layers.
As depicted in FIG. 1A, a prior art grasper-type instrument is depicted with jaw-electrodes engaging opposing side of a tissue volume with substantially thick, dense and non-uniform fascia layers underlying its exterior surface, for example, a large diameter blood vessel. As depicted in FIG. 1A, the fascia layers f prevent a uniform flow of current from the first exterior tissue surface s to the second exterior tissue surface s that are in contact with electrodes 2a and 2b. The lack of uniform bi-polar current across the fascia layers f causes non-uniform thermal effects that typically result in localized tissue desiccation and charring indicated at c. Such tissue charring can elevate impedance levels in the captured tissue so that current flow across the tissue is terminated altogether. FIG. 1B depicts an exemplary result of attempting to create a weld across tissue with thick fascia layers f with a prior art bi-polar instrument. FIGS. 1A-1B show localized surface charring c and non-uniform weld regions w in the medial layers m of vessel. Further, FIG. 1B depicts a common undesirable characteristic of prior art welding wherein thermal effects propagate laterally from the targeted tissue causing unwanted collateral (thermal) damage indicated at d.
What is needed is an instrument working end that can utilize Rf energy in new delivery modalities: (i) to weld or seal tissue volumes that are not uniform in hydration, density and collagenous content; (ii) to weld a targeted tissue region while substantially preventing collateral thermal damage in regions lateral to the targeted tissue; (iii) to weld a transected margin of a bundle of disparate anatomic structures; and (iv) to weld a transected margin of a substantially thick anatomic structure.
The object of the present invention is to provide an instrument and working end that is capable of transecting tissue and highly compressing tissue to allow for controlled Rf energy delivery to the transected tissue margins. The objective of the invention is to effectively weld tissues that have thick fascia layers or other layers with non-uniform fibrous content. Such tissues are difficult to seal since the fascia layers can prevent uniform current flow and uniform ohmic heating of the tissue.
As background, the biological mechanisms underlying tissue fusion by means of thermal effects are not fully understood. In general, the delivery of Rf energy to a captured tissue volume elevates the tissue temperature and thereby at least partially denatures proteins in the tissue. One objective is to denature such proteins, including collagen, into a proteinaceous amalgam that intermixes and fuses together as the proteins renature. As the treated region heals over time, the so-called weld is reabsorbed by the body""s wound healing process.
In order to create an effective weld in a tissue volume dominated by the fascia layers, it has been found that several factors are critical. It is necessary to create a substantially even temperature distribution across the targeted tissue volume to create a uniform weld or seal. Fibrous tissue layers (i.e., fascia) conduct Rf current differently than adjacent less-fibrous layers, and it is believed that differences in extracellular fluid content in such adjacent tissues also contribute greatly to the differences in ohmic heating. It has been found that by applying very high compressive forces to fascia layers and underlying non-fibrous layers, the extracellular fluids migrate from the site to collateral regions. Thus, the compressive forces can make resistance more uniform regionally within the engaged tissue.
Another aspect of the invention provides means for creating high compression forces over a very elongate working end that engages the targeted tissue. This is accomplished by providing a slidable extension member that defines channels therein that engage the entire length of elongate guide members that guide the extension member over the tissue. The extension member of the invention thus is adapted to provide multiple novel functionality: (i) to transect the tissue, and (ii) contemporaneously to engage the transected tissue margins under high compression within the components of the working end. Optionally, the extension member can be adapted to carry spaced apart longitudinal electrode surfaces for delivery of Rf current to each transected tissue margin from the just-transected medial tissue layers to surface layers.
Of particular interest, the invention further provides first and second jaw engagement surfaces with electrodes that define stepped resistive gradients across the electrodes"" engagement surfaces for controlling Rf energy delivery to the engaged tissue. It has been found that precise control of ohmic heating in the engaged tissue can be accomplished by having electrode surfaces that define a plurality of portions with differential resistance to electrical current flow therethrough.
In another embodiment of the invention, the working end includes components of a sensor system which together with a power controller can control Rf energy delivery during a tissue welding procedure. For example, feedback circuitry for measuring temperatures at one or more temperature sensors in the working end may be provided. Another type of feedback circuitry may be provided for measuring the impedance of tissue engaged between various active electrodes carried by the working end. The power controller may continuously modulate and control Rf delivery in order to achieve (or maintain) a particular parameter such as a particular temperature in tissue, an average of temperatures measured among multiple sensors, a temperature profile (change in energy delivery over time), or a particular impedance level or range.
Additional objects and advantages of the invention will be apparent from the following description, the accompanying drawings and the appended claims.